Disclosed is an economical method of recycling polycondensation resin waste.
Polycarbonates are a high value material that is used in product applications like lenses, compact discs, construction materials, automobile parts, chassis of office appliances, camera bodies, bottles, fibres, etc. The demand for these resins is increasing.
After use, these products are processed by burning or burying them underground as waste. However, recovery and recycling of these wastes may be advantageous from the viewpoint of environmental protection and/or cost, and especially if the recycled product could be reused.
For example, polycarbonate resin wastes are used after partial remolding. When remolding is carried out, it has the problems of lowering of molecular weight, deterioration of physical properties like strength, and discoloration of the material, all of which make large-scale reapplication difficult. The material is discarded after one reuse. Thus, it is not recycling in the true sense.
Various methods for reusing polycarbonate resin wastes are known. For example, Kokai no. 6-220184 discloses a method for reuse of polycarbonate, wherein waste polycarbonate is dissolved in monophenol and made to undergo depolymerisation (disintegration) in the presence of a quaternary ammonium compound or quaternary phosphonium compound catalyst to form a mixture of oligocarbonate, and diphenol. The oligocarbonate is then polycondensed.
Kokai no. 7-316280 has mentioned a recycling method where the aromatic dihydroxy compound or diaryl carbonate obtained by disintegration of aromatic polycarbonate resin waste, is used again as a raw material for the preparation of aromatic polycarbonate resin. In this method, aromatic polycarbonate raw material of aromatic dihydroxy compound and diaryl carbonate are recovered by transesterification reaction between aromatic polycarbonate waste and aromatic monohydroxy compound, through the following steps: (A) In step I aromatic polycarbonate resin and aromatic monohydroxy compound are subjected to transesterification reaction, (B) in step II, diaryl carbonate containing aromatic monohydroxy compound is 1separated by distillation from the reaction product of the Step 1, (C) in step 3 where aromatic monohydroxy compound is added to aromatic dihydroxy compound left as residue in step 2 and is heated to form their addition product and the addition product is separated after it is deposited out as crystals by cooling, and (D) step 4 in which the crystals obtained in Step 3 are heated and melted, and aromatic monohydroxy compound is distilled off to obtain aromatic dihydroxy compound.
The above methods may be described as the depolymerization of high molecular weight polycarbonates made with high energy processes energy, wherein the depolymerization process also requires high energy inputs. Thus, such process is not energy efficiency.
Furthermore, Kokai no. 11-152371 mentions a method of solid phase polymerisation where the polycarbonate is not depolymerized. In this method, after dissolving the polycarbonate waste in a solvent, the dissolved polycarbonate component is crystallised. However, this process requires solvent and is not satisfactory from the viewpoint of energy efficiency and environmental hygiene.
It would thus be advantageous to provide a method of recycling polycarbonate resin waste wherein the waste is used in a fusion polymerisation apparatus to obtain polycarbonate resin with high-energy efficiency.